Recursize unsized types cause ICE

[jamii]

http://is.gd/o35wcP

Expected: Not sure, maybe some error about fat pointers growing unboundedly.

Actual: Uncommenting either line results in ICE.

What I am trying to achieve is something like:

struct Node: {
  population: u16,
  children: [Option<Node>; popcount(population)]
}

This general pattern (lengths depending on prior values) is useful for building data structures. It does not seem to be covered by DST and otherwise requires unsafe.

[frewsxcv]

Visiting for triage: this is still an issue

[apasel422]

Triage: Still an issue.

[Mark-Simulacrum]

Changing the code to not use unsized enums which currently aren't supported fixes this ICE. Since this no longer ICE's, I'm going to close.

struct Tree(u16, [Option<Box<Tree>>]);

struct Node<T: ?Sized> {
    population: u16,
    children: T,
}

struct Tree2(Node<Tree>);

fn main() {
    use std::mem::size_of;
    use std::sync::atomic;
    println!("{:?}", size_of::<&Tree>());
    println!("{:?}", size_of::<&Tree2>());
}

rustc 1.19.0-nightly (2d4ed8e0c 2017-05-03)
warning: field is never used: `population`
 --> <anon>:4:5
  |
4 |     population: u16,
  |     ^^^^^^^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

warning: field is never used: `children`
 --> <anon>:5:5
  |
5 |     children: T,
  |     ^^^^^^^^^^^
  |
  = note: #[warn(dead_code)] on by default

warning: unused import: `std::sync::atomic`
  --> <anon>:12:9
   |
12 |     use std::sync::atomic;
   |         ^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(unused_imports)] on by default

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